The present invention relates generally to components for use in radio frequency (RF) and microwave designs, and more particularly, to an integrated filter balun.
In radio frequency (RF) and microwave designs, there is often the need to convert a signal from a single-ended regime to a differential regime. For example, in a receiver design, an antenna typically provides a signal that is in a single-ended form. However, there is typically a point in the signal path where a differential signal is expected by a particular circuit or component. In this regard, a circuit is needed to convert the single-ended signal to a differential signal that is acceptable to that circuit or component.
Similarly, there is often the need to convert a signal from a differential regime back to a single-ended regime. For example, in a transmitter design, a differential signal that is being provided by an amplifier is provided to an antenna for transmission. However, the antenna typically has a single-ended input. Consequently, a circuit is needed to convert the differential signal provided by the amplifier to a single-ended signal that is acceptable to the antenna.
Accordingly, an important component in RF and microwave design is the balanced to unbalanced circuit (or xe2x80x9cbalunxe2x80x9d) that provides the required functionality to convert a signal between a single-ended regime to a differential regime and visa-versa.
Another important component in a designer""s toolbox is the filter. The increase in wireless communications services is forcing more and more channels into less frequency spectrum. To avoid interference, these systems must comply with very stringent filtering requirements. Consequently, the filter component is important for helping these systems to handle the power levels and to provide the needed isolation.
Currently, the filter component and balun component are provided as separate components with their own respective housing. These separate components are then typically soldered to a printed circuit board to achieve a desired functionality. The separate filter component and balun component increase system cost, occupy valuable board space and require extra design effort.
Since many designs are implemented in portable handsets or other portable computing devices, the size and weight of the components that are utilized in a design are important considerations. Consequently, it is desirable for there to be a technology that integrates the filter functionality and the balun functionality into a single component, thereby saving board space, decreasing system costs, and simplifying the design effort.
Based on the foregoing, there remains a need for an integrated component that overcomes the disadvantages set forth previously.
According to one embodiment of the present invention, a component that includes a first structure that is integrated with a second structure is provided. The first structure is a lumped balanced to unbalanced circuit (balun) and the second structure is a resonator-based filter. The function of the balun is to move a signal from a differential form to a single ended form or from a single ended form to a differential form. The component has an area that is comparable to the area needed to implement the balun alone. However, the component now provides a filter function. Preferably, the substrate of the first structure also acts as a substrate for the second structure.
According to one embodiment, the component of the present invention includes a filter with a single ended input and a single ended output. When the filter is the first stage, the balun has a single ended input for coupling to the output of the filter and a differential output. When the filter is the second stage, the balun has a differential input and a single ended output for coupling to the input of the filter.
According to another embodiment, the component of the present invention includes a filter with a differential input and a differential output. When the filter is the first stage, the balun has a differential input that is coupled to the output of the filter and a single ended output. When the filter is the second stage, the balun has a single ended input and a differential output coupled to the input of the filter.
In one embodiment, the filter is implemented with a resonator-based filter that includes a single-ended input and a single-ended output, such as a half-ladder filter. Alternatively, the filter may be implemented with a resonator-based filter that includes differential inputs and differential outputs, such as a full-ladder filter or a lattice filter, or a combination thereof.
In one embodiment, the balun is implemented with transmission lines that act as impedance transformers. Alternatively, the balun is implemented with lumped equivalent circuits.